This invention relates to a proportional mixing valve for mixing a hot and a cold fluid that includes a fail-safe mechanism for shutting off hot fluid flow when the temperature of the fluid exiting the valve exceeds a predetermined set point.
Mixing valves and fail-safe mechanisms in water and other fluid supply systems are well known. They are typically employed to control the maximum fluid temperature to a predetermined set point, which is usually a temperature, that is safe for human skin upon prolonged exposure. For example, hot water from water heaters typically has a temperature of 140.degree. F. to 160.degree. F. with a maximum temperature of 180.degree. F. At 140.degree. F., a child can be scalded if the skin is exposed for one second. However, if the water temperature is reduced to 120.degree. F. continuous exposure for five minutes is required to scald the skin.
In domestic applications, and in many commercial uses, it is desirous that the maximum hot water temperature from a shower, tub or basin outlets be set at a level that prevents serious burning or scalding of the skin. Oftentimes, a water faucet is allowed to run in a full flow hot water condition to purge cold water resting in the supply line to the faucet. A child or other unsuspecting person would be scalded if they were to contact the water once the cold water is purged. Thus, mixing valves are often used in the supply piping to basin, tub, or shower faucets in order to temper the hot water supply. Tempering the hot water supply at these point-of-use locations allows higher temperature water to continue to be produced by a water heater and used at locations where it is necessary, such as the washing machine or dishwasher.
While mixing valves temper the hot water supply under normal operating conditions, a fail-safe mechanism is necessary to isolate the flow of hot water when the supply of cold water fails. Serious injury could result to a child if, for instance, the cold water supply fails while the child is taking a shower, causing the water temperature to increase to its maximum supply temperature. Thus, fail-safe mechanisms can provide an added protective feature when combined with a mixing valve that is used to temper hot water.
Previous patents of mixing valves and fail-safe devices for hot fluid have employed various techniques. For example, U.S. Pat. No. 4,299,354 to Ketley discloses a thermally operated mixing valve. The temperature of the fluid is controlled via a thermally responsive control member that varies the flow of the cold fluid as needed to temper the hot water to the desired preset temperature. If the cold water supply fails or is interrupted, the control member reacts to either restrict or nearly isolate hot water flow. The valve is typically located at the point-of-use of the fluid supply since the user must manually operate the control member with an actuator to obtain fluid at a temperature less than the preset maximum temperature.
Another type of device is disclosed in U.S. Pat. No. 4,480,784 to Bennett and U.S. Pat. No. 3,938,741 to Allison. Each of these patents discloses safety devices for isolating water flow to an outlet when the water temperature exceeds a predetermined set point. Both devices are employed in the apparatus, which discharges the water, such as a showerhead. The Bennett devices employs a thermostatic cup that expands to constrict flow, but allows the hot water to drip so that the device continues sensing the water temperature. The Allison device includes a temperature responsive mechanism with a valve attached to one end that isolates flow when the water temperature exceeds a given operating temperature.
The foregoing prior art suffers from several drawbacks. For instance, the mixing valve device must be located near where the flow of fluid is controlled by the user. The devices also rely on a modulating control member to temper the hot water supply whose setting is controlled by the user's manipulation of an actuator. In some valves, the fail-safe devices are required to be on or near a water supply system is required to temper the hot water supply temperature.
Another desirable feature absent from these prior systems is the ability to adjust the fluid temperature at the point-of-use outlet. Different maximum temperatures may be desirable at different discharge outlets, such as a kitchen sink versus a workroom tub.
What is needed, therefore, is a mixing valve assembly, which does not require modulating elements in order to temper the hot fluid supply. What is also needed is a mixing valve assembly, which includes a fail-safe mechanism that allows the valve to be used in virtually any location in a domestic or commercial water supply or fluid supply system.